This invention relates to a hydraulic lash adjuster for use in the valve operating mechanism of a four-cycle engine.
Hydraulic lash adjusters are being increasingly used in various four-cycle engines because they enable zero lash operation of the valve operating system, low noise operation and minimal maintenance. When a hydraulic lash adjuster (hereinafter referred to as "the lash adjuster") is used in a parallel multicylinder or a single cylinder enginer where the cylinder section is oriented upwardly, or in a V-engine, there are generally no problems. However, when it is used in a horizontal opposed engine, for instance, where the cylinder section is disposed horizontally, or in an engine where it is disposed aslant close to a horizontal position, the lash adjuster is turned sideways or upside down. Because of this, oil in the high pressure chamber for giving static pressure reaction to the slidably incorporated plunger flow out thereby rendering the lash adjuster inoperative.
In order to avoid this problem, a construction has been conceived for a horizontal engine wherein the lash adjuster is installed upright or only somewhat aslant to an extent so as not to cause trouble. Such a construction is shown in FIGS. 1 to 4. The axis O.sub.2 of the rocker arm support 1a of the rocker arm shaft 1 is offset in the amount of "h" in reference to the center O.sub.1 of the rocker arm shaft 1. The rocker arm 2 is supported by the rocker arm support 1a (that is, the offset portion) and performs zero lash by means of lash adjuster 4 engaged with the engaging cavity 1c provided on not-offset portion 1b. That is, it performs operation where contact between cam 5 and the rocker arm 2 will not develop clearance. The head 4b of the plunger 4a of the lash adjuster 4 has been formed into a spherical shape.
In the conventional construction as described above, contact of the lash adjuster 4 with the engaging cavity 1c of the rocker arm shaft 1 is made by using the bottom 4d of the lash adjuster 4 (that is, the bottom of the body 4c) for the exhaust valve 6 side, for instance, and by using the head 4b of the lash adjuster 4 (that is, the head of the plunger 4a) for the intake valve 7 side on the other hand, so that:
(1) In the lash adjuster 4(A) of the bottom 4d contact type, because the head 4b of the plunger 4a is spherical, the head 4b abuts on the plug 8 by a point contact as shown in FIG. 3 for disadvantage of durability with respect to wear;
(2) In the lash adjuster 4(B) of the head 4b contact type, because the plunger head 4b is in contact with the engaging cavity 1c of the rocker arm shaft 1 and because the engaging cavity 1c of the lash adjuster 4(B) is formed into an almost spherical shape as shown in FIG. 4, force in the direction of arrow (a) acts according to movement of the plunger 4a to injure the smoothness of mutual sliding between the plunger 4a and lash adjuster body 4c. Because of spherical shape of the head 4b resulting in only point contact, it also is disadvantageous in durability with respect to wear; and
(3) Because the rocker arm 2 turns, it is necessary to provide a member for receiving axial thrust of the rocker arm shaft 1, which results in a disadvantage of cost increase.
This invention was produced in view of such circumstances and the object thereof is to eliminate the above described disadvantages by removably providing a plunger cap on the plunger head of the hydraulic lash adjuster .